Celiac disease is an autoimmune disorder in which the body overreacts to gluten, a protein found in wheat, rye and barley. When celiacs ingest gluten, their immune system attacks the hairlike villi lining their small intestines, hampering their ability to absorb nutrients to disperse to the bloodstream.

While diarrhea, bloating, constipation and vomiting are short-term hallmarks of celiac disease, the malabsorption of nutrients can lead to longer-term problems, including weakened bones, anemia and neurological problems. Celiacs are also at increased risk of gastrointestinal cancers, among other diseases. Left unchecked, celiac disease can even lead to death. Recent research suggests that the disease is far more common than had been believed, affecting as many as one in 133 people.

But once you get that diagnosis, the remedy is obvious: Eliminate gluten from your diet, and watch your symptoms vanish. Better yet, strict avoidance of gluten over time can reverse damage the disease has already done. Not only does diarrhea cease, intestines heal.

Vanessa Maltin was a 21-year-old junior studying journalism at George Washington University in 2004 when she learned she had celiac disease. Maltin had suffered chronic headaches all her life; nobody could figure out why. When at last a blood test pointed toward celiac disease, Maltin says she was "depressed for about six weeks. I lived in a college dorm, and it was hard not to eat the same things, like pizza and Chinese food, as my college friends."

Maltin's depression was short-lived. She cut out gluten, and "within two months, I felt all better. The first day I woke up and didn't have a headache, I was so blown away, I never missed eating gluten again." Today Maltin is the food and lifestyle editor for Delight magazine, devoted to all things gluten-free. She's also a member of the Washington Area Celiac Sprue Support Group, which has about 800 members. (Sprue is another name for celiac.)

Avoiding gluten was far trickier then than it is today. Whereas only a few small manufacturers produced gluten-free products just a few years back, gluten-free is big business now, with major companies such as General Mills, Betty Crocker and Wal-Mart offering no-gluten foods. That growth is fueled in part by consumers who, while not having received a diagnosis of celiac disease, find they don't tolerate gluten well and would just as soon avoid it. Gluten-free products are generally more expensive than their gluten-containing equivalents; some celiacs learn to rely heavily on meats, fruits and vegetables, and other foods that naturally contain no gluten.

Dining out remains problematic. While Maltin says many restaurants, particularly in the Washington area, have begun offering gluten-free dishes, celiac diners have to remain vigilant, as gluten lurks not just in the obvious beer, bread and other baked goods but also in sauces, marinades, salad dressings and other places you might not expect to find grains.

And one small mistake can lead to misery. "If I accidentally get some gluten," she says, " . . . it's like having food poisoning. I have a four- or five-day reaction, and the headaches come back." Maltin now calls restaurants ahead of her visit to discuss her dietary needs and makes it a habit to speak with the chef before ordering her meal.

As Maltin is well aware, the improved digestion that comes with eliminating gluten often means the body takes in more calories. "All of a sudden, you're absorbing everything," she says. "After diagnosis, people typically gain 20 to 40 pounds." Maltin gained weight herself after her diagnosis, moving from a size 2 to a size 4.

(She's currently planning an October 2010 wedding, with a gluten-free reception. The one exception: Her fiance, who Maltin says is extremely supportive of her gluten-free living, wants to drink Guinness at the event. Though gluten-free beers are available, Maltin's fine with his choice.)

Biopsy of the intestine's lining via endoscopy remains the most definitive way to diagnose the disease. Blood tests can reveal whether a person's body has developed antibodies to gluten proteins, a sign that celiac disease may be present. Genetic analyses, including a new saliva test developed by Prometheus Laboratories, can determine whether one has the genetic makeup associated with celiac; this at-home test has the advantage of being able to rule out celiac altogether.

As with all autoimmune diseases, it's believed that celiac occurs when a person who has a genetic predisposition encounters some environmental trigger that moves the faulty immune response into action. But celiac is the only autoimmune disease for which that environmental trigger -- in this case, gluten -- has been identified, according to Alessio Fasano, director of the University of Maryland Center for Celiac Research.

That makes celiac disease an enticing research subject. As Fasano explains in a fascinating article in the current issue of Scientific American, celiac serves as a perfect model for studying the phenomenon of autoimmunity. Researchers can establish control groups for experiments, testing treatments on celiacs who continue to eat gluten and those who don't and comparing the two groups' responses.

Fasano has discovered that people with autoimmune diseases tend to have abnormalities in their intestines that make them permeable -- what he calls "leaky guts." That permeability may be the factor that gives environmental triggers access to the immune systems of genetically susceptible people. Fasano has launched research of a drug called larazotide, which inhibits the action of zonulin, a protein that increases intestinal permeability. Early results on people with celiac disease have been promising.

Until the mysteries of their disease are solved, celiacs will have to continue watching what they eat. But as Maltin notes, the celiac life doesn't have to be all that restrictive. "We travel all over the world and eat great food," she says. In fact, "the hardest place is in the airport. I always bring my own food with me."

Check out Tuesday's Checkup blog post, in which Jennifer explores the world of gluten-free food. Subscribe to the Lean & Fit newsletter by going to http://www.washingtonpost.com/health.